Obesity is at endemic proportions in the United States and worldwide, and it increases the risk of several other diseases such as non-alcoholic fatty liver disease (NAFLD), type II diabetes, hypertension, and depression. It even reduces our readiness for military conflict as the number of available recruits is decreased. Recent data indicates that the development of NAFLD and obesity is about more than just overeating, but also chemical exposure. Exposure to select pharmaceuticals or environmental toxicants called obesogens that alter the way individuals allocate nutrient resources, especially the storage of white adipose tissue. There are several potential mechanisms by which obesogens may increase NAFLD or obesity, and one potential mechanism may involve the inhibition of cytochrome P450 (CYP) activity through lower CYP expression or chemical inhibition. The cytochrome P450s (CYPs) are key enzymes involved in the detoxification of numerous chemicals including steroids, bile acids, pharmaceuticals, fatty acids, and environmental pollutants. The CYPs in families 1-3 are the key xenobiotic detoxifying CYPs. They are often highly inducible and therefore alterations in their activity can cause changes in the metabolism of endogenous chemicals such as steroids, bile acids, or fatty acids. The Cyp2b and Cyp3a subfamily are highly inducible through xenobiotic sensing nuclear receptors such as CAR and PXR. Interesting, recent reports indicate that these receptors are also involved in metabolic diseases such as NAFLD and obesity. We consider it likely that some of the CYPs they regulate are also involved in NAFLD and obesity. We propose an innovative hypothesis that inhibition of specific cytochrome P450s plays a putative role in the NAFLD/obesity epidemic. We have very recently developed a novel Cyp2b9/10/13-triple-knockout mouse by Crispr/Cas9 to test whether loss or inhibition of hepatic Cyp2b members increases the likelihood that individuals will develop NAFLD and obesity (Aim 2). In addition, we will test whether the previously developed Cyp3a-null mouse is also susceptible to obesity (Aim 1). Last, we will investigate whether environmental pollutants that inhibit Cyp2b or Cyp3a enzymes increase NAFLD and obesity during treatment with normal or high-fat diets (Aim 3). We are investigating the Cyp3a and Cyp2b subfamilies because the Cyp3a subfamily is the most abundant hepatic CYP subfamily and the most important in the metabolism of a number of xenobiotics, and therefore subject to induction and inhibition. The Cyp2b subfamily was previously implicated as a potential factor in unsaturated fatty acid metabolism and we have observed reduced hepatic clearance of unsaturated fatty acids coupled with higher serum triglycerides and cholesterol, and greater body weight and white adipose tissue weight in older Cyp2b compromised mice (Cyp2b-knockdown). Overall, the purpose of this project is to test whether alterations in Cyp2b and Cyp3a activity (such as chemical inhibition) can alter the allocation of fatty acids and in turn cause NAFLD and obesity.